1. Field of the Invention
The present invention relates to a system for performing Device to Device (D2D) direct communication. More particularly, the present invention relates to a method and an apparatus for transmitting a packet between devices.
2. Description of the Related Art
Advances in communication and computing technologies have provided users with more sophisticated communication systems. With the continuing development of such communication systems, users desire a service enabling them to easily obtain and share information with other users at anytime. Recently, as smart phones and tablet Personal Computers (PCs) have emerged on the market, an environment that enables a user to obtain and share various information via a wireless communication system has grown in importance. However, the method of obtaining and sharing information of the related art is applicable to only a wireless communication system where an infrastructure has been established. As such, it is difficult to efficiently provide real-time information due to complexity or temporal delay of a wireless communication system.
Accordingly, a Device to Device (D2D) direct communication service has emerged. In the D2D direct communication service, a communication link between devices is formed by directly sharing information in a space where a communication infrastructure has not been established.
Devices supporting the D2D direct communication service preferentially obtain synchronization with a peripheral device and then explore a peripheral device via a determined point and resource to obtain information of the explored peripheral device. After that, respective devices generate a Connection Identifier (CID) for connection with a device to directly communicate based on the obtained peripheral device information. Also, the respective devices perform inter-device connection scheduling, rate scheduling, and traffic transmission based on the generated CID.
FIG. 1 illustrates scheduling and data transmission of a D2D system according to the related art.
As illustrated in FIG. 1, respective devices 111, 112, 113, 114, 115, 116, 117, and 118 perform inter-device connection scheduling 100, rate scheduling 103, and traffic transmission 105 based on generated CIDs. More specifically, devices 111 to 118 transmit/receive signaling and determine whether to transmit/receive data based on an inter-device interference circumstance during a relevant traffic transmission section 105 at the connection scheduling step 100. For example, when each of transmission devices 1 to 4 (111 to 114) transmits signaling for scheduling, each of reception devices 5 to 8 (115 to 118) measures the signal intensity of a corresponding transmission device and the interference signal intensity of a peripheral device based on a CID to determine whether to perform data transmission/reception or abandon data transmission during a relevant traffic transmission section 105 based on the measurement result. At this point, the reception device 7 117 having the same CID as that of the transmission device 3 113 detects an interference signal from the transmission device 1 111 having a CID of a higher priority than that of the CID of the reception device 7 117, and abandons data reception during the relevant data transmission section 105. In contrast, the reception device 6 116 having the same CID as that of the transmission device 2 112 detects an interference signal from the transmission device 4 114 having a CID of a lower priority than that of the CID of the reception device 6 116, but does not abandon data reception during the relevant data transmission section 105 because the CID of the reception device 6 116 is higher. In this case, the transmission device 4 114 that interferes with the reception device 6 116 and the reception device 8 118 abandon data transmission/reception during the relevant data transmission section 105.
As described above, the D2D direct communication service of the related art determines a link to transmit/receive data during a relevant data transmission section via a connection scheduling process. However, this method does not consider the size of data transmitted by each device. Rather, this method uses a resource of a fixed size so that there is a limitation in effective use of a limited resource.
That is, since control of an infrastructure does not exist in the case of a D2D direct communication service, it is difficult to variably operate the size of a transmission resource between devices and, for D2D transmission, a D2D direct communication system uses a resource of a fixed size. Therefore, since the size of transmission data can vary in the D2D direct communication system, there exists a need for an alternative apparatus and method that can effectively utilize a resource depending on the varying size of data.